Phase-locked loops are widely used in integrated circuits such as, for example, when it is required to generate an oscillator signal with a voltage controlled oscillator (VCO) under control of a reference input signal from a reference clock. In a phase-locked loop driven system, it is often required to keep the system ongoing for a short time while the reference clock is missing; for example, if the reference clock is faulty or has disappeared. During the time when the reference clock is missing, the system should be able to drive into a safety recover mode. A simple recover mode could be to switch to a redundant reference clock. However, it would be desirable to keep the output of the PLL stable in frequency and phase while the reference clock is missing. The invention has been devised with the foregoing in mind.